1. Field of the Invention
This invention relates to the field of switching voltage regulators, and particularly to control schemes for such regulators.
2. Description of the Related Art
Switching voltage regulators are widely used due to their high efficiency, which makes them particularly suitable for use in battery-powered devices such as laptop computers. However, despite the inherent efficiency of switching regulators, efforts are ongoing on many fronts to achieve ever better efficiencies, so that the life of the battery in such battery-powered devices can be extended.
A switching regulator operates by switching current through an inductor on and off repetitively. A transistor typically serves as the switch, the state of which is controlled with a fixed-frequency control signal applied to the transistor""s base or gate. The regulator""s output voltage is typically maintained by adjusting the duty ratio of the control signal provided to the transistor. This technique tends to provide a satisfactory efficiency level when the regulator is driving a heavy load with an output current at or near the regulator""s rated maximum. However, when the load decreases to a moderate or light level, the efficiency of the regulator also decreases; this is because the switching components continue to be toggled at the same fixed frequency, while the regulator provides less output current.
A switching voltage regulator is presented which overcomes the problems noted above, providing high efficiency operation for heavy loads, as well as moderate and light loads.
The novel regulator employs a xe2x80x9cdual modulationxe2x80x9d scheme to control the regulator""s switching components. A control circuit monitors load current. If the load decreases, the control circuit reduces both the duty ratio and the frequency of the control signals which operate the switching transistors. Similarly, an increasing load current results in an increase in the duty ratio and frequency of the control signals. By varying both duty ratio and frequency with a varying load current, the regulator maintains a high efficiency level over a wider output current range than can be achieved with fixed-frequency control signals.
In a preferred embodiment, the regulator employs three operating modes. For heavy loads, the switching components are operated at a constant frequency. For moderate-to-light loads, the dual modulation control scheme is used. For very light loads, the regulator enters a xe2x80x9cpulse-skippingxe2x80x9d mode which can achieve very low operating frequencies to further improve efficiency.
The invention may be used with switching regulators which use peak current mode, average current mode, or voltage mode control, as well as buck, buck-boost, and boost power stages.
Further features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.